Field of the Invention
The present disclosure relates to a method for manufacturing a light emitting device, and more particularly, to a method for manufacturing a light emitting device with a lens disposed to cover a light emitting element.
Description of the Related Art
Light emitting devices using a semiconductor chip (light emitting element), such as a light emitting diode, are widely used because of easy reduction in size and high light emission efficiency.
Some of these light emitting devices have, for example, a lens (sealing portion serving as a lens) for refracting a light emitted from the semiconductor chip in a desired direction in order to obtain a large amount of light in a specific direction, such as in an upper surface direction of a mounting substrate or the like. This kind of light emitting device with the lens is widely used for many applications, including illumination and backlight.
The lens used in such a light emitting device is normally disposed over the mounting substrate to cover the light emitting element. Most of the light emitted from the light emitting element refracts through the lens, and travels from the upper surface of the lens in the desired direction.
Such arrangement of the lens, however, brings most areas of a lower surface of the lens into contact with the surface of the mounting substrate. As a result, a part of the light emitted from the light emitting element, especially, light directed downward, reaches the mounting substrate through the lens. This is because when n1 is a refractive index of a translucent material, such as glass or resin forming the lens, and n2 is a refractive index of material forming the substrate, the total reflection does not occur as n2 is larger than n1, or a critical angle causing the total reflection becomes large due to a small difference between the refractive indexes n1 and n2 even though n1 is larger than n2.
Although a part of the light reaching the mounting substrate is reflected to return the lens again, most of the light reaching the mounting substrate then hits the mounting substrate and is absorbed in the substrate. The absorption of the light in the mounting substrate can be relieved by increasing the reflectivity of the surface of the mounting substrate. However, even by use of the known strategies for relieving the light absorption, a considerable amount of the light is absorbed in the mounting substrate, which may disadvantageously reduce a light extraction efficiency.
For this reason, a light emitting device is known which includes the lens (especially, the bottom surface of the lens) extended to the outside of the substrate in the planar view.
In such a light emitting device, the light emitting element is mounted on the mounting substrate. The light emitting element and the upper surface of the mounted substrate are disposed within the lens, and the lower surface of the mounting substrate protrudes (exposes) from the bottom surface of the lens.
A part of the bottom surface of the lens that extends to the outside of the mounting substrate is in contact with air. Air has a small refractive index, which leads to a large difference between the refractive index n1 of the translucent material, such as glass or resin, forming the lens, and a refractive index nair of the air, thereby decreasing a critical angle causing the total reflection to a small value. As a result, most of the light emitted from the light emitting element and reaching the bottom surface of the lens can be reflected to suppress the amount of the light exiting out of the bottom surface of the lens to the outside.
Thus, the light emitting device with the lens (especially, the bottom surface of the lens) extended to the outside of the mounting substrate in the planar view can realize high light extraction efficiency, particularly, the high light extraction efficiency from the upper surface of the lens.
For example, methods disclosed in JP 2011-077491 A and JP 2007-273764 A are known as a method for manufacturing such a light emitting device with the lens extended to the outside of the mounting substrate in the planar view.
In the method disclosed in JP 2011-077491 A, a plurality of mounting substrates with light emitting elements mounted thereon is spaced apart from each other on a lower mold (lower side mold). A spacer is disposed between the adjacent mounting substrates with a spacing therebetween. Then, an upper mold (upper side mold) having at its lower surface a concave portion corresponding to the shape of the lens to be obtained is prepared. The upper mold is brought into contact with and press-fitted to the lower mold so as to place a light emitting element within the concave portion while charging a sealing member before hardening (material for the lens) into the concave portion. After that the sealing member is hardened to obtain the light emitting device with a desired lens shape.
The method disclosed in JP 2007-273764 A involves preparing an upper mold (upper mother mold) that holds amounting substrate with a light emitting element mounted thereon over a lower surface of the mounting substrate, and a lower mold that has a concave portion corresponding to the shape of the lens to be obtained over an upper surface of the mounting substrate, a concave portion corresponding to the shape of the lens to be obtained, by using a chuck. The upper side mold and the lower side mold are brought into intimate contact with each other, whereby the mounting substrate and the light emitting element are disposed in the concave portion (chamber). Then, after decompressing the inside of the concave portion, a mixed solution including a monomer of thermosetting resin and polymerization catalyst is supplied into the concave portion. Then, the mixed solution is hardened, thereby obtaining a light emitting device with a lens having a desired shape.
In use of the method disclosed in JP 2007-077491 A, however, the sealing member before hardening comes around behind the lower surface of the mounting substrate, whereby a resin film might be formed at the lower surface of the mounting substrate of the light emitting device obtained.
The formation of the resin film on a wiring layer provided at the lower surface of the mounting substrate might cause the problem of conduction failure. In order to avoid the occurrence of the conduction failure, it is necessary to add a step of removing the resin film after formation of the lens.
On the other hand, in use of the method disclosed in JP 2007-273764 A, the bottom surface of the obtained lens may not become a flat surface or a smooth curved surface due to the shrinkage of resin upon hardening, which may cause asperity on the bottom surface (for example, whereby asperity may be formed on the bottom surface of the lens in the cross-sectional view). As a result, the total reflection may not occur in some cases.